This invention relates to electrophotography and more particularly is concerned with the application of liquid toner to an electrostatic image and to the processing of electrostatic images using liquid toner.
There are a number of difficulties in the satisfactory application and removal of liquid toner; disadvantages of known systems include:
(a) waste of toner which causes both unnecessary purchase of expensive toner and unnecessary labour in the dirty task of replenishing the machine with fresh toner;
(b) non-uniformity of toning over the area being processed;
(c) traps in the toner feed path in which toner may move only slowly, which may permit changes in the properties of the slow moving toner relative to that which is delivered quickly, which again causes non-uniformity in toning; and
(d) failure to remove liquid toner completely before fusing from areas which should be clear, thus leading to grey or speckled areas in the eventual image which should be white.
The present invention aims to alleviate or ameliorate these difficulties, and is especially applicable to making copies which require very fine detail, for example in producing miniature or micro-copies and especially when copying onto TEP film (transparent electrophotographic film) such as the TEP materials supplied commercially by James River Graphics of Massachussetts, United States, Kodak, and others. The invention is also applicable to any other electrophotographic process and electrophotographic equipment using liquid toner. The invention is also of particular value when up-dating is carried out, i.e., when a piece of material receives an image covering less than its whole area, that image is developed and may be viewed, and at a later time the image-carrying material is re-exposed and processed to receive an additional image. In these circumstances, it is important that the exposure and processing of the first image have a negligible effect on that part of the image-receiving material which will later receive another image, and likewise that the exposure and processing of the second image have a negligible effect on the first image.